Development Of Transverse Cracks Research Articles

Corrosion of Yb2SiO5/Yb2Si2O7/Si EBCs against Na2SO4 + 25 wt%NaCl molten salt at 1350 ℃

The reaction behaviors and corrosion mechanisms of tri-layer Yb2SiO5/Yb2Si2O7/Si EBCs were explored in Na2SO4 + 25 wt%NaCl molten salt environment at 1350 °C. Results showed that the molten salt rapidly penetrated the Yb2SiO5 layer and then reacted with the Yb2Si2O7 layer to form SiO2-riched Na-Yb-Si-O glass phase. The reaction product of glass phase diffused to the EBCs surface through the cracks and reacted with Yb2SiO5 to form Yb2Si2O7. The reaction of Yb2Si2O7 caused the development of transverse cracks, which eventually led to the failure of the EBCs. Moreover, the Yb2SiO5 layer exhibited better corrosion resistance than the Yb2Si2O7 layer.

Efficiency of an Improved Grouted Corrugated Duct (GCD) Connection Design for Precast Concrete Bridge Pier: Numerical and Parametric Study

In this study, finite element analysis (FEA) has been conducted for an improved grouted corrugated duct (GCD) connection design with a reserved recess in bridge footing. This study aims to understand the damage progression mechanism and to evaluate the contribution of each component in the improved GCD connection design. Numerical model based on the experimental results are first created, validated and calibrated. It is found that the confining effect (support and friction force) provided by recess sidewall keeps the connection in good integrity. It also prevents early deformation and early development of transverse cracks along the connection interface, which further avoids the damage concentration at connection joint, transfers the plastic hinge region. Parametric study is then carried out by considering different recess depths, cushion thicknesses, recess diameters, and mortar strengths. The effect of recess details on mechanical behavior is thus studied. Recess depth can be designed as 6–20% of the column section size to ensure a higher upper limit of overall strength and ductility, and it also influences the stress distribution area of the joint local. The stiffness and strength of recess control the local damage, while has limited impact on the overall performance. In addition, preliminary suggestions on the GCD design of recess depth, thickness of mortar cushion, recess diameter, the strength of mortar are proposed.

ANALYSIS OF THE REASONS FOR CRACKING PIPES OF THE BOILER OF THE RECOVERY

8-381X 
 Abstract. Formulation of the problem. One of the main tasks of production is reliable and trouble-free operation of equipment. In the oxygen-envelope process, when cast iron is purged, a large amount of carbon monoxide CO is emitted in the converter, which has a high temperature of more than 1 700 °С of the outgoing gases. The envelope gases in the waste heat boiler are cooled. Converter gas output is characterized by cyclic unevenness In this case, uneven heating of the walls of the boiler pipes occurs. By circulation pumps, chemically purified water is supplied for forced cooling of the boiler walls. When raising the outgoing gases, the cooling water is converted to pars by its subsequent supply to the consumer. The study is dedicated to solving the scientific and applied problem for the reasons for the formation of defects and the identification of cracks in the pipes of the recovery boiler.The purpose of the work. To investigate the causes of the development of transverse cracks in the pipelines of the recovery boiler by various methods of non-destructive testing, to use the methods of scanning microscopy to analyze the microstructure, mechanical tests, and the magnetic properties of structural carbon steel. Conclusions. One of the main reasons for the appearance of massive cracks in the pipes of cylindrical caissons is thermal fatigue caused by high thermal loads. Transverse cracks have the character of thermal fatigue failure, which is confirmed by changes in the ferrite-pearlite structure of the metal, resulting from uneven local cooling of the walls of the caisson. The reasons for the violation of the water circulation in the boiler are the pressure drop in the boiler and a sharp discharge, the load is the release of water from the boiler.

Evaluation of surface roughness and bond-slip behavior of new textured epoxy-coated reinforcing bars

Epoxy-coated reinforcing bars are widely used in bridge decks to mitigate the corrosion of reinforcing steel. Research and practical experience both showed that the smooth epoxy coating significantly reduces the bond between concrete and reinforcing steel, which often results in the early development of transverse cracks in bridge decks. To solve this problem, the Illinois Department of Transportation (IDOT) proposed a new type of textured epoxy-coated (TEC) reinforcing bars with applied roughness to improve the bond between concrete and steel while providing corrosion protection. This study investigates the surface roughness of six different types of TEC bars and how it impacts the bar’s bond-slip behavior with concrete. First, the surface roughness of the TEC bars is compared with that of uncoated black bars (BLK) using 2-D parameters Ra, Rz, and 3-D parameters Sa and Sz. Second, direct pull-out tests are conducted on concrete specimens with embedded 1) BLK, 2) smooth epoxy-coated (SEC), and 3) all six TEC bars to compare their bond characteristics. Finally, a 3-D finite element model is developed and calibrated to simulate the bond-slip behavior of TEC bars embedded in concrete. The results show that the average surface roughness of TEC bars is 3–4 times that of the uncoated bars. Further, TEC bars generally exhibit higher slip resistance than the uncoated and smooth epoxy-coated bars.

Cracking models for HMA overlay treatment of composite pavements in Louisiana

ABSTRACT Cracking is one of the primary forms of distress suffered by hot-mix asphalt (HMA) overlay of composite pavements. Pavement cracking affects the ride quality and pavement service life by allowing water and debris to penetrate through the pavement structure. This paper presents the development of transverse cracking and longitudinal cracking performance models for overlay treatment of composite pavements in the state of Louisiana. Various factors that affect the cracking performance of overlay treatment were identified. Such factors include equivalent single axle load (ESAL), thickness of HMA and Portland cement concrete (PCC), functional classification of roadways, and newly developed temperature indexes. Regression analyses were performed to identify those factors and to develop cracking prediction models. In order to better predict the pavement service life, the existing condition of the pavement was also utilised through the models. The developed models provided an acceptable agreement between the measured and predicted crack values. It was found that the predictions were improved when the existing pavement condition was incorporated in the models. The resulting cracking models could be used by Louisiana Department of Transportation and Development (LADOTD) as a good pavement management tool for timely pavement maintenance and rehabilitation actions to maximise benefits, driver’s comfort, and safety.

Establishment of Prediction Models of Asphalt Pavement Performance based on a Novel Data Calibration Method and Neural Network

This paper aims to develop models to forecast the deterioration of pavement conditions including rutting, roughness, skid-resistance, transverse cracking, and pavement surface distress. A data quality control method was proposed to rebuild the performance data based on the idea of longest increasing or decreasing subsequences. Neural network (NN) was used to develop the five models, and principal component analysis (PCA) was applied to reduce the dimension of traffic variables. The influence of different input variables on the model outputs was discussed respectively by comparing their mean impact values (MIV). Results show that the proposed NN models demonstrated great potential for accurate prediction of pavement conditions, with an average testing R-square of 0.8692. The results of sensitivity analysis revealed that recent pavement conditions may influence the future pavement conditions significantly. Rutting and roughness were sensitive to pavement age and maintenance type. The materials of original pavement asphalt layer were highly relevant to the prediction of pavement roughness, skid-resistance, and pavement surface distress. Moreover, traffic loads obviously affected the pavement skid-resistance and transverse cracking. Pavement and bridge had different effect on surface distress. The material of the base has a remarkable impact on the initiation and development of transverse cracks. Disease treatment in terms of pavement cracking—such as sticking the cracks, excavating and filling the cracks—shows a high MIV in the prediction model of transverse cracking and pavement surface distress.

On micro–meso relations homogenizing electrical properties of transversely cracked laminated composites

A practical way to track the development of transverse cracking in a laminated composite is to monitor the change of its electrical resistance. Yet, the relations between transverse cracking and the global modification of resistivity is still unclear that makes difficult to interpret these non-destructive-testing results. Here, we introduce the homogenization process that defines at the meso scale an equivalent homogeneous ply that is energetically equivalent to the cracked one. It is shown that this equivalent ply mainly depends on the cracking level while it can be considered independent on the rest of the laminated structure. The direct consequence is that the meso scale is a pertinent one to perform the homogenization. Then, non-destructive electrical measurements can be considered as a reliable technique to access meso scale damage indicators.

Analyzing Influence Factors of Transverse Cracking on LTPP Resurfaced Asphalt Pavements through NB and ZINB Models

The negative binomial (NB) and zero-inflated negative binomial (ZINB) models were employed to simulate the development of pavement transverse cracks on asphalt overlays and to evaluate the influence of different designs of asphalt overlays on crack development. Pavement transverse crack data were collected from 15 long-term pavement performance (LTPP) SPS-5 test sites. Analyzed factors include traffic level, overlay thickness, mixture [using reclaimed asphalt pavement (RAP) or virgin], intensity of surface preparation (mill or no mill) before overlay, total thickness of pavement, and freeze index. Analysis results indicate that the NB and ZINB models were effective in simulating the development of pavement transverse cracks by addressing the overdispersion. In addition, the ZINB model outperformed the NB model by explaining the excess zeros in the cracking count data to capture both the initiation and propagation of cracking. The regression analysis indicates that mill before overlay is effective in retarding the initiation of cracks, but not the propagation of cracks. Thicker overlay appears to reduce transverse cracking. High traffic level or using RAP is likely to increase the number of transverse cracks. Total thickness of pavement and freeze index are not significant for the development of transverse cracks.

Modeling Fracture and Delamination of Spray-Applied Fire-Resisting Materials under Static and Impact Loads

A specially developed two-dimensional cohesive zone finite element (CZFE) scheme is applied to simulate the fracture and delamination phenomena that occur in spray-applied fire-resisting material (SFRM) on steel structures. A cohesive zone material model for the SFRM is introduced and utilized to model both the internal cohesion in SFRM and the interfacial adhesion at the steel-SFRM interface. The CZFE model is validated by comparing predictions from the model with results from an adhesion test conducted at ambient temperature. The validated model is successfully applied to simulate the spontaneous initiation and propagation of cracks in the SFRM under static and impact loads. Results from the numerical studies indicate that the proposed model is capable of predicting the initiation and propagation of cracks within the insulation material and at the interface. The results show that the development of transverse cracks in the insulation layer help prevent further delamination of the SFRM. Also, it was found that for larger thicknesses of insulation, delamination occurs at less direct tension or flexural stresses. Results from impact simulations show that there is an optimum insulation thickness for resisting the delamination induced by impact loads.

Effect of PG XX-34 on Transverse Cracking in Minnesota

The Minnesota Department of Transportation (DOT) adopted the use of performance-graded (PG) asphalt binders in 1997. In 1999 the Minnesota DOT required PG XX-34 binders for all new (not overlay) bituminous construction with the objective of reducing the amount of transverse cracking. Pavement management data were used to track the development of transverse cracking on PG XX-34 projects. The transverse cracking rate of the PG XX-34 projects was then compared with the cracking rates for similar projects from the pre-PG era. The comparison found that after 7 years of service, transverse cracks on the PG projects were developing at approximately 1/10th the rate experienced before performance grading was implemented.

Effect of transverse cracks on the elastic properties of high temperature angle-ply laminated composites

The development of transverse cracks can be detrimental to the stiffness and dimensional stability of composite laminates. In this investigation, a modified shear lag analysis, taking into account the concept of stress perturbation function, is employed to evaluate the effect of transverse cracks on the stiffness reduction in high temperature angle-ply laminated composites. The results present well the effect of high temperature and the fibre orientation of the outer layers on the degradation of mechanical properties of the angle-ply polymer composite laminates.

Helicoidal Composites

The behavior of a carbon/epoxy composite material is examined for improved mechanical properties using a design based on a helicoidal architecture. Helicoidal composites with 40 layers, [180/170/160/150/140/130/120/110/100/90/80/70/60/50/40/30/20/10/(0)/2] S are used. Through-thickness reinforcement was provided in some of the specimens by the stapling with stainless steel staples. For the helicoidal arrangement, the gradual change in in-plane properties in each layer results in lower interlaminar shear stresses. It is found that the specimen with helicoidal stacking sequence has better debonding resistance and improved damage tolerance. In a tensile test, it is shown that the helicoidal architecture results in higher energy absorption due to limits on the development of transverse cracks. In the circular plate test, the helicoidal specimen shows the highest load and energy absorption. The impact test shows the highest penetration resistance. Some specimens with through-thickness reinforcement were manufactured and characterized. The reinforced laminate presents higher load carrying capacity, better delamination resistance and a graceful failure.

平織強化複合材料の損傷進展に及ぼす積層位相ずれの影響

Woven fabric composites have superior mechanical properties such as ductility and tear strength, compared with unidirectional fiber reinforced composites. As the application of their laminates to main parts of various structures increases, the damage behaviors of woven fabric composites become a subject of considerable interest for recent years. Although the mechanical behaviors of laminates are affected strongly by stacking configuration, their mechanism has not been completely revealed due to the geometric complexity of fabric architecture. In this paper, the effect of mismatch of stacking phase on damage development has been investigated numerically by a three-dimensional finite element analytical code based on damage mechanics. Our finite element analysis has an advanced point in anisotropic post-failure constitutive equation considering mesoscale failure modes. The mechanical behaviors of plain woven fabric composites under on-axial tensile load have been analyzed for 2-layered laminates with different stacking phase. As a result, it has been recognized that out-of-phase laminate shows stronger performance compared with iso-phase laminate. Additionally, it has been revealed that 2-layered laminate with 1/4 phase mismatch in perpendicular direction to tensile load shows slower damage occurrence and development of transverse cracks in wefts, and that ones with 1/4 phase mismatch in parallel direction show more rapid damage progress than iso-phase laminate.

Transverse cracking and delamination in cross-ply glass-fiber and carbon-fiber reinforced plastic laminates: Static and fatigue loading

A review of developments and understanding of transverse cracking and delamination in cross-ply laminates is presented. First, experimental investigations reported in the literature for analyzing the development of transverse cracking are considered. Next, characteristics of different models for evaluating the stress distribution in the damaged laminates are developed. It is shown how these models associated with the statistical description of strength or energy released in the 90° plies make it possible to describe the development of transverse cracking in monotonic or fatigue loading. According to the nature of cross-ply laminates, transverse cracking is not, however, sufficient for describing the development of transverse cracks in 90° plies in the case of monotonic loading. In this case, the delamination process induced at transverse crack tips is to be considered for describing the experimental results. There are 108 references in this review article.

Analysis of damage mode transition in a cross-ply laminate under uniaxial loading

The aim of this work is to study the transition from one damage mode to another. The three damage mechanisms usually observed in [0 m /90 n ] s long fibre cross-ply laminates with organic matrix are transverse cracking, which appears first, longitudinal cracking and/or delamination. The proposed analytical model is meant to describe the development of transverse cracks and to predict the order of initiation of subsequent damage modes; it relies on the strain energy release rate associated with each damage mechanism.

Development of transverse cracking in cross-ply laminates during fatigue tests

The purpose of this paper is to analyse the progressive development of transverse cracking in cross-ply laminates subjected to uniaxial fatigue tests. First, a finite-element analysis shows how an analytical model which considers a progressive shear through the thickness of the 0° layers can be used for evaluating the stress field in the case of progressive cracking across the specimen width. The paper then presents a simulation of the progression of the transverse cracking, based on statistical distributions along the specimen length for crack initiation and across the specimen width for crack growth across the specimen width. The simulation process is applied to glass-fibre/epoxy cross-ply laminates and the results obtained are compared with experimental results.

Performance of Transverse Cracking in Jointed Concrete Pavements

Environmental effects and repetitive traffic applications can lead to the development of transverse cracks in jointed concrete pavements. Maintaining adequate aggregate interlock load transfer across these cracks is essential to preserving the functional and structural integrity of these pavements. The objectives of this study were to determine the design parameters that significantly affect transverse cracking and to demonstrate methods available for evaluating cracked pavements. Field data collected from in-service jointed concrete pavements located throughout southern Michigan were used to accomplish these objectives. Joint spacing, coarse aggregate type, shoulder type, and pavement temperature were found to have significant effects on transverse crack development and/or performance. The surface texture of crack faces was assessed using a promising new test method called volumetric surface texture testing. Volumetric surface texture results provided an indication of the aggregate interlock potential of pavements containing various aggregate types. Three performance parameters capable of mechanistically characterizing crack performance were discussed. A relatively simple procedure was described for determining these parameters and evaluating crack conditions. Field data were also used to demonstrate and validate a voids' analysis procedure. This procedure estimates the potential for loss of support near cracks and joints, thus allowing for proper rehabilitation actions to be taken prior to the manifestation of additional distresses.

Structure, morphology, and properties of PBZT and methyl pendant PBZT fibers

The structure, morphology, and properties of the methyl pendant PBZT fiber have been studied with variations in thermomechanical treatment. For comparison, selected studies on PBZT fibers have also been carried out. Crosslinking in the methyl pendant PBZT fiber occurs in the 450–550°C range under free annealing, leading to a nonfibrillar structure. Recoil compressive strength, loop strength, torsional modulus, and the transverse compressive strength of the tension heat-treated MePBZT fiber are 50 to 100% higher compared to the comparably heat-treated PBZT fiber. Compressive strength and other mechanical properties could not be measured on highly crosslinked free annealed samples, as such samples showed significant transverse cracks. Reasons for the development of transverse cracks have been discussed. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 305–314, 1999

Investigation of Design Parameters Affecting Transverse Cracking in Jointed Concrete Pavements

Environmental effects and repetitive traffic applications can lead to the development of transverse cracks in jointed concrete pavements (JCPs). Maintaining adequate aggregate interlock load transfer across these cracks is essential to preserving the functional and structural integrity of these pavements. The objectives of this study were to determine the design parameters that significantly affect transverse cracking and to demonstrate methods available for evaluating cracked pavements. Field data collected from in-service JCPs located throughout southern Michigan were used to accomplish these objectives. Joint spacing, coarse aggregate type, shoulder type, and pavement temperature were found to have significant effects on transverse crack development and/or performance. The surface texture of crack faces was assessed using a promising new test method called Volumetric Surface Texture (VST) testing. VST results provided an indication of the aggregate interlock potential of pavements containing various aggregate types. Three performance parameters capable of mechanistically characterizing crack performance were discussed. A relatively simple procedure was described for determining these parameters and evaluating crack condition. Field data were also used to demonstrate and validate a voids-analysis procedure.

2D and 3D numerical models of transverse cracking in cross-ply laminates

Two numerical models, 2D and 3D, have been developed in order to study the behaviour of cross-ply laminates during multiplication of transverse cracks. The displacement and stress fields have been evaluated by the finite-element method in an elementary cell which is characteristic of regularly spaced cracks. The longitudinal stiffness reduction has then been deduced as a function of the transverse crack multiplication. In the case of quasi-static tensile tests, the 2D model has been used to estimate the initiation and development of transverse cracking. The different numerical results obtained have been compared with experimental results.